1. Field
This disclosure is directed to mobile communications using service data, and more particularly to improved mobile communications using Unstructured Supplementary Service Data (USSD) for an Internet Protocol Multimedia Subsystem (IMS) in a network.
2. Related Art
IP Multimedia Subsystem (IMS) is an architectural framework for delivering internet protocol (IP) multimedia to mobile stations. IMS handles several types of media (e.g., audio and video) in a synchronized way from the user's point of view via Internet Protocol (IP). IMS may involve multiple parties, multiple connections, and the addition or deletion of resources and users within a single communication session. Voice Call Continuity (VCC) is an IMS application that provides capabilities to transfer voice calls between a circuit switched (CS) domain and a packet switched (PS) domain. IMS Centralized Services (ICS) Control Channel (hereafter “ICCC”) is a logical signaling channel used to transport control signaling between the ICS User Equipment (UE) and an IMS network when the ICS UE accesses the IMS services via the CS domain. Unstructured Supplementary Service Data (USSD) is a standard for transmitting information over Global System for Mobile Communications (GSM) signaling channels and is generally associated with real-time or instant messaging type phone services.
Conventionally, when a mobile station (MS) is engaged in a call or other Man-Machine Interface (MMI) activity, the MS rejects any USSD because such Supplementary Service is considered a lower priority. Accordingly, the USSD for carrying out data is not a reliable transport for ICCC and no viable alternative methods are available to address this issue.